There was many german C64 games even from Rainbow Arts which was never sold outsite germany. For example: Danger Freak, Bad Cat, To be on Top...but as far as I know there where almost always in english and if not, I've never played them.;)

"Oil Imperium" from "Reline", an economy game with action parts could be one of this games but maybe there was also an english version. I only had a german copy of a friend, even uncracked with code requester. But there are possibly some more games.